1. Field of the Invention
The present invention generally relates to a pneumatic tire monitoring device, and more particularly to a wireless pneumatic tire monitoring device which has antennas disposed within the brake oil line.
2. Description of the Related Art
Wireless tire pressure monitors have been proposed so that the tire pressures of vehicle tires can be checked in the passenger compartment. The monitor includes transmitters disposed within the wheels and a receiver attached to the body of the vehicle. Each transmitter measures the tire pressure of each corresponding tire and performs wireless transmission of the measured pressure data. The receiver receives the data from each transmitter and displays the data information of each tire on a display which is located, for example, at the dashboard in front of the driver""s seat.
A typical tire pressure monitor includes four transmitters correspondingly disposed within the four tires of a vehicle. Since the output strength of radio waves or electromagnetic waves from each transmitter is limited by local communication laws and cannot be greatly increased, the receiver has four reception antennas that respectively correspond to the four transmitters to ensure reception of weak radio signals from the transmitters. Accordingly, the reception antennas are typically located in the vicinity of the tires, which have the built-in transmitters, for example, in or near the fenders (cf. Japanese Unexamined Utility Model Publication No. 2-74204).
The reception antennas described in the above Japanese Utility Model are arcuate wire antennas, which extend along the fenders. Each wire antenna induces voltage mainly by an electric field of radio waves. However, most vehicle bodies have metal fenders, which are likely to influence the electric field of radio waves. The electric field of radio waves attenuates in the vicinity of metal materials. Therefore, the wire antennas attached to the fenders cannot efficiently receive radio waves from the transmitters.
To improve the efficiency of receiving radio waves, each wire antenna must be separated from the metal surface of the corresponding fender as far as possible. However, even if the distance between a wire antenna and the metal surface is varied slightly, the performance of the wire antenna varies greatly. This makes it difficult to maintain the quality of the monitor. Also, once the wire antenna is separated from the metal surface of the corresponding fender too far, the wire antenna may interfere with the corresponding tire.
Furthermore, U.S. Pat. No. 6,304,172 B1, entitled xe2x80x9cReceiver of Inflation Pressure Monitorxe2x80x9d issued on Oct. 16, 2001 to Katou et al., discloses a tire pressure monitor including wheel transmitters and a receiver with magnetic field type loop antennas. The loop antennas induce voltage mainly by a magnetic field of radio waves and thus efficiently receive radio waves from the transmitters. However, the loop antenna is expensive and complicated and cannot be readily attached to the fender.
Accordingly, there exist needs for providing a tire monitoring device having an antenna which can be readily attached to the vehicle and efficiently receives the radio waves from the sensors disposed within the tires of the vehicle.
It is an object of the present invention to provide a tire monitoring device having an antenna which can be readily attached to the vehicle and efficiently receives the radio waves from the sensors disposed within the tires of the vehicle.
It is another object of the present invention to provide an antenna disposed in a vehicle for efficiently receiving the electromagnetic waves.
To achieve the aforementioned objects, the present invention provides a monitoring device for monitoring pneumatic tires of a vehicle. The vehicle has a plurality of tires each with a brake device being connected to a brake system of the vehicle through a brake oil tube. The monitoring device comprises a sensor module, an antenna, and a decoding module. The sensor module is attached to the tire of the vehicle for sensing a condition of the tire and transmitting a radio signal including the pressure and temperature condition. The antenna is disposed within the brake oil tube for receiving the radio signal which is transmitted from the sensor module. The decoding module electrically connected to the antenna for processing the received radio signal.
According to another object of the present invention, an antenna is provided for being disposed in a vehicle. The vehicle has a plurality of tires each with a brake device being connected to a brake system of the vehicle through a brake oil tube. The antenna comprises an antenna portion and a transmission line. The antenna portion is used for receiving an electromagnetic signal from an external signal source, and the transmission line electrically connected to an external circuit, wherein the antenna portion and a portion of the transmission line are attached to the brake oil tube.